1. Field of the Invention
This invention relates to a semiconductor package which accommodates a semiconductor device therein.
2. Description of the Related Art
A semiconductor package provided with a package main body including a base portion having a first surface and a second surface positioned on a side opposite to the first surface and a semiconductor device accommodating portion provided on the first surface, in which a semiconductor device is accommodated, and electric terminals provided in the semiconductor device accommodating portion and electrically connected to the semiconductor device accommodated in the semiconductor device accommodating portion and exposed to an outer surface of the semiconductor device accommodating portion, has been conventionally known.
The semiconductor device is formed by mounting a desired circuit pattern on a surface of a substrate formed of substrate material typified by silicon, where a large amount of heat is generated from the circuit pattern during operation of the semiconductor device. When the temperature of the circuit pattern exceeds a certain temperature, the circuit pattern cannot play in a desired performance.
In such a conventional semiconductor package, at least the base portion of the package main body is configured by material with high heat conductivity, for example, copper, aluminum, copper alloy, or aluminum alloy, in order to radiate heat which is generated by the semiconductor device. Heat which is generated by the semiconductor device accommodated in the semiconductor device accommodating portion is transferred to the package main body, mainly to the base portion, and the heat is further radiated to an object with which the package main body, mainly the base portion, comes in contact, for example, a semiconductor package supporting body on which the base portion is placed and supported, air surrounding the package main body, or the like.
In recent years in which high integration of a circuit pattern mounted on a semiconductor device progresses and a heat quantity generated by the semiconductor device increases, various structures for improving heat transfer efficiency of the semiconductor package have been proposed.
Jpn. Pat. Appln. KOKAI Publication No. 2004-288949 discloses one example of the structure for improving heat transfer efficiency such as described above. In a semiconductor package disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-288949, a graphite sheet is in close contact with a second surface of a base portion of a package main body. The graphite sheet has high heat conductivity and it rapidly diffuses heat transferred from the second surface of the base portion of the package main body in a direction extending along the second surface, so that heat transfer efficiency from the base portion of the package main body to an object adjacent thereto is enhanced.
Jpn. Pat. Appln. KOKAI Publication No. 2001-144237 discloses another example of the structure for improving heat transfer efficiency such as described above. In this structure for improving heat transfer efficiency, a plurality of graphite sheets and a plurality of sheet metals are alternately stacked on one another. The sheet metal increases a heat transfer amount due to its large heat capacity, while the graphite sheet improves heat radiation from the sheet metal owing to its large heat conductivity.
In the structure for improving heat transfer efficiency described in Jpn. Pat. Appln. KOKAI Publication No. 2004-288949, when the base portion of the package main body of the semiconductor package is fixed to a predetermined position on a surface of a semiconductor package supporting body by screws, the graphite sheet is sandwiched between the second surface of the base portion and the predetermined position on the surface of the semiconductor package supporting body, so that the graphite sheet is brought in close contact with the second surface of the base portion and the predetermined position on the surface of the semiconductor package supporting body.
In the fixation by the screws such as described above, however, evenness of the degree of close contact of the graphite sheet with the second surface of the base portion of the package main body of the semiconductor package and the predetermined position on the surface of the semiconductor package supporting body is reduced easily. That is, heat transfer efficiency from the second surface of the base portion to the predetermined position on the surface of the semiconductor package supporting body becomes uneven easily on these surfaces. In addition, heat transfer efficiency of the graphite sheet in a thickness direction thereof is smaller than that in a direction along the surface of the graphite sheet.
In the structure for improving heat transfer efficiency described in Jpn. Pat. Appln. KOKAI Publication No. 2004-288949, therefore, sufficient cooling effect cannot be exerted to increase of heat quantity generated by a semiconductor device in recent years.
In the structure for improving heat transfer efficiency described in Jpn. Pat. Appln. KOKAI Publication No. 2001-144237, the plurality of graphite sheets and the plurality of sheet metals alternately stacked to one another are mutually brought in close contact with one another and fixed to one another by screws, glue, or adhesive.
Because of increase in the number of graphite sheets which are used and use of the plurality of sheet metals, the structure for improving heat transfer efficiency described in Jpn. Pat. Appln. KOKAI Publication No. 2001-144237 is improved in radiation efficiency as compared with the structure for improving heat transfer efficiency described in Jpn. Pat. Appln. KOKAI Publication No. 2004-288949. In the fixation by the screws, glue, or adhesive as described above, however, such a fact that evenness of the degree of mutual close contact between the plurality of graphite sheets and the plurality of sheet metals is reduced easily remains. That is, mutual heat transfer efficiency between the plurality of graphite sheets and the plurality of sheet metals becomes uneven easily. Further, the heat transfer efficiency of the graphite sheet in the thickness direction is smaller than that in the direction along the surface of the graphite sheet.
Accordingly, in the structure for improving heat transfer efficiency described in Jpn. Pat. Appln. KOKAI Publication No. 2001-144237, sufficient cooling performance cannot be played to the increase in heat quantity generated by the semiconductor device in recent years. Since the thickness of each of the plurality of sheet metals mutually fixed to the plurality of graphite sheets by the screws, glue or adhesive is relatively large, the thickness of the abovementioned structure becomes relatively large.